PT Burden Tests 2

[CuriousElectron]

Greetings,
Has anyone done offline Potential Transformer burden testing? Is offline PT burden testing more challenging to do than an online testing? Just wanted to hear from your experience.
Thanks,
EE

 

[pwrengrds]

If I wanted to check the burden, I just powered it up with a relay test set and measured it with an ammeter, same with the CT, push 5 amps and measure the voltage. Usually not that much of an issue with the newer relays.

 

[che12345]

Dear Mr. CuriousElectron (Electrical)(OP)6 Sep 22 16:35
"...#1. Has anyone done offline Potential Transformer burden testing? #2. Is offline PT burden testing more challenging to do than an online testing? ".
#1. It is possible to carry out PT burden test online or offline.
#2. Offline, being not exposed to the system voltage would be of lower risk.
#3. I take it that the (burden) of a PT is made up mainly of [a resistor and a contactor in series]. The resistor is the sum of contact and wire resistances and the coil winding Cu resistance, which are independent of the frequency. The contactor coil is equivalent to an inductor, which is defendant on both the frequency and whether the contactor is closed or open. Note: the coil inductance increases very much when the iron-core pulled into position. The pull-in VA is about 10x holding VA.
#4. Online test: Caution, HV risk !. Measure the secondary voltage and current with contactor/relay contact closed.
#4.1. Offline test: Test at the same system frequency. Increase the test set voltage to the same as the PT secondary voltage and take current readings with contactor closed.
#5. Size the PT burden (VA) rating =/> 10x the (VA) taken with the contactor closed (pulled in ).
Che Kuan Yau (Singapore)

 

[scottf]

CuriousElectron-

When you ask about "burden testing", are you asking about testing to ensure that the connected burden doesn't exceed the burden rating of the VT or are you asking about the test method (normally used on CTs) where the burden placed on the secondary is changed (via a test set or switch box) and the change in output is observed to ensure the unit is performing as it should?